1. Field of the Invention
The present invention relates to an inline pressure sensor for measuring a pressure in a liquid member.
2. Description of Related Art
Conventionally, a pressure sensor has been used for measuring a pressure in a liquid member (liquid or gas) which flows in a piping section. Such a pressure sensor is commonly called a single-port pressure sensor which is attached to a branching piping section which is branched from the piping section for flowing the liquid member. However, in such a single-port pressure sensor, the branching piping section causes a dead volume (liquid pool) in which the liquid member remains undesirably. In such a case, there is a problem if the liquid member decomposes. Also, if an expensive liquid member flows in the piping section, the dead volume in which the liquid member remains undesirably may cause a substantial amount of wasted liquid member; thus, there is a problem in that the unnecessary expense may be incurred.
In order to solve the above problem, an inline pressure sensor has been developed in which a pair of coupling ports are formed at both ends of the pressure sensor such that the coupling ports are disposed via a coupling section so as to be on the same line as the piping section in which the liquid member flows. In such an inline section to which the pressure sensor should be attached.
Such a conventional inline pressure sensor 1 (hereinafter called a “pressure sensor”) has a structure shown in a cross section in FIG. 5. According to the pressure sensor 1, a flexible cap member 4 is disposed in a housing 3 which is connected to the piping section which is not shown in the drawing so as to be orthogonal to a coupling member 2 which is connected to the piping section so as to be aligned with the piping section. A liquid 5 such as an antifreeze fluid is sealed in the cap member 4 such that a pressure which is applied on a pressure sensing element 6 in a sensor section via the cap member 4 and the liquid 5 may be measured (see Japanese Unexamined Utility Application, First Publication No. Sho 61-197534, pages 3-9, and FIG. 1). Here, an inner casing space of which the cross sectional area is larger than a cross section of the piping section is formed beneath the pressure sensing element in a flow path in the above conventional inline pressure sensor. A volume in the inner casing space is smaller than that in the branching piping section in the single port pressure sensor. However, such an inner casing space is upwardly blocked while branching upwardly from the flow path which is disposed so as to be aligned with the piping section. Therefore, such an inner casing space may cause a liquid pool in which the liquid member remains undesirably.
If an expensive liquid member is circulated, such a liquid member remaining thereinside increases the dead volume; thus, more liquid member is necessary. Therefore, such a dead volume may cause a substantial amount of waste liquid member; thus, there is a problem in that a unnecessary expense may be incurred. Also, such a liquid member remaining thereinside is not preferable because the liquid member which is supposed to be used for a beverage or a medicine decomposes while remaining thereinside for a long period and this is not desirable. Therefore, it has been desired that an inline pressure sensor be developed which can minimize the dead volume.